Bipolar tissue ablation in accordance with a predefined periodic set of time slots

ABSTRACT

A method for applying bipolar ablation pulses, the method includes positioning multiple electrodes of a catheter in contact with tissue of an organ. The tissue is ablated using the multiple electrodes in accordance with a predefined pattern including a periodic set of time slots. Each of the time slots defines (i) an electrode-pair (EP), (ii) a waveform of one or more bipolar ablation pulses (BAPs) applied to the tissue by the EP, and (iii) a duration of the time slot. The time slots are applied sequentially, and the pattern further includes at least one time slot that is empty.

FIELD OF THE INVENTION

The present invention relates generally to medical devices, andparticularly to methods and systems for bipolar tissue ablation.

BACKGROUND OF THE INVENTION

Various techniques for ablating an extended area of heart tissue byapplying irreversible electroporation (IRE) pulses are known in the art.

For example, U.S. Pat. No. 10,470,822 describes a system for estimatinga three-dimensional treatment volume for a device that applies treatmentenergy through a plurality of electrodes defining a treatment area, thesystem comprising a memory, a display device, a processor coupled to thememory and the display device, and a treatment planning module stored inthe memory and executable by the processor.

U.S. Patent Application Publication No. 2019/0336207 describes a systemthat includes a pulse waveform generator and an ablation device coupledto the pulse waveform generator. The ablation device includes at leastone electrode configured for ablation pulse delivery to tissue duringuse. The pulse waveform generator is configured to deliver voltagepulses to the ablation device in the form of a pulsed waveform. Thepulsed waveform can include multiple levels of hierarchy, and multiplesets of electrodes can be activated such that their pulsed delivery isinterleaved with one another.

SUMMARY OF THE INVENTION

An embodiment of the present invention that is described herein providesa method for applying bipolar ablation pulses, the method includespositioning multiple electrodes of a catheter in contact with tissue ofan organ. The tissue is ablated using the multiple electrodes inaccordance with a predefined pattern including a periodic set of timeslots. Each of the time slots defines (i) an electrode-pair (EP), (ii) awaveform of one or more bipolar ablation pulses (BAPs) applied to thetissue by the EP, and (iii) a duration of the time slot. The time slotsare applied sequentially, and the pattern further includes at least onetime slot that is empty.

In some embodiments, a first electrode of a first EP is positionedbetween second and third electrodes of a second EP. In otherembodiments, each of the time slots includes a time gap scheduled beforeor after the one or more BAPs. In yet other embodiments, the BAPsinclude irreversible electroporation (IRE) BAPs.

In an embodiment, the EPs of the time slots have a same inter-electrodedistance. In another embodiment, a first EP of a first time slot of thepredefined pattern includes a first electrode and a second electrode,and a second EP of a second time slot of the predefined pattern includesthe first electrode and a third electrode.

In some embodiments, the predefined pattern includes at least one timeslot positioned between the first and second time slots. In otherembodiments, positioning the catheter includes positioning a lassocatheter.

There is additionally provided, in accordance with an embodiment of thepresent invention, a system including a catheter, a pulse generator, anda processor. The catheter including multiple electrodes, which areconfigured to make contact with tissue of an organ. The pulse generatoris configured to generate one or more bipolar ablation pulses (BAPs).The processor is configured to ablate the tissue using the multipleelectrodes in accordance with a predefined pattern including a periodicset of time slots that are applied to the tissue sequentially. Each ofthe time slots defines (i) an electrode-pair (EP) selected from themultiple electrodes, (ii) a waveform of the one or more BAPs applied tothe tissue by the EP, and (iii) a duration of the time slot, and thepattern further includes at least one time slot that is empty.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

FIG. 1 is a schematic, pictorial illustration of a catheter-basedposition-tracking and irreversible electroporation (IRE) ablationsystem, in accordance with an exemplary embodiment of the presentinvention;

FIG. 2 is a schematic pictorial illustration of a tip section of an IREcatheter having multiple electrodes, and architecture for applying IREpulses to selected electrodes thereof, in accordance with an exemplaryembodiment of the present invention; and

FIG. 3 is a flow chart that schematically illustrates a method forapplying bipolar IRE ablation pulses to tissue, in accordance with anexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

Irreversible electroporation (IRE) may be used, for example, fortreating arrhythmia by ablating tissue cells using high-voltage pulsesapplied to the tissue. Cellular destruction occurs when thetransmembrane potential exceeds a threshold, leading to cell death andformation of a lesion. In IRE-based ablation procedures, also referredto herein as an IRE ablation for brevity, high-voltage bipolarelectrical pulses are applied, for example, to pairs of electrodes incontact with tissue to be ablated, so as to form a lesion between theelectrodes, and thereby to treat arrhythmia in a patient heart.

Sometimes, a lasso-type catheter having multiple electrodes, may be usedfor performing IRE ablation over an extended area. Due to the lassoshape of the catheter, when applying bipolar IRE pulses to pairs ofelectrodes sequentially or simultaneously, one or more electrodes thatare not intended to be energized, may undesirably touch an energizedelectrode, and consequently, may disrupt the outcome of the IREablation, and in severe cases, may be harmful to the patient.

Embodiments of the present invention that are described hereinbelowprovide improved techniques for applying the IRE bipolar pulses using anablation protocol that improves the patient safety.

In some embodiments, in an IRE ablation procedure using a lasso-typecatheter, a physician positions multiple electrodes of the catheter incontact with a target tissue, such as pulmonary vein of a patient heart.Subsequently, the physician may use a processor that controls an IREablation system for ablating the tissue using the multiple electrodes inaccordance with a predefined pattern comprising a periodic set of timeslots.

In some embodiments, the time slots are applied sequentially, and eachof the time slots defines (i) an electrode-pair (EP) selected from amongthe multiple electrodes, (ii) a waveform of one or more bipolar ablationpulses (BAPs), also referred to herein as “IRE ablation pulses,” areapplied to the tissue by the EP, and (iii) duration of the time slot.Note that the term “periodic” refers to one or more repetitions of thesame predefined pattern. For example, a given predefined pattern mayhave three time slots, wherein one or more BAPs are applied sequentiallyto first, second and third EPs, during first second and third timeslots, respectively. Subsequently, the given predefined pattern isrepeated with applying the one or more BAPs to the first EP of the firsttime slot and so on.

In some embodiments, the electrodes of different EPs are interleaved,such that a first electrode of a first EP is positioned between secondand third electrodes of a second EP. Each of the time slots comprises atime gap scheduled before or after the one or more BAPs, so that duringthe time gap IRE ablation pulses are not applied to the target tissue.

In some embodiments, the pattern further may comprise at least one timeslot that is empty, in other words, IRE ablation pulses are not appliedto any EP during the duration of the empty time slot.

The disclosed techniques improve the safety in various bipolar ablationprocedures applying bipolar pulses applied to a target tissue having abroad area, by controlling the position of the bipolar ablation pulsesapplied to the target tissue.

System Description

FIG. 1 is a schematic, pictorial illustration of a catheter 21 basedposition-tracking and irreversible electroporation (IRE) ablation system20, in accordance with an exemplary embodiment of the present invention.

In some embodiments, system 20 comprises a deflectable tip section 40that is fitted at a distal end 22 a of a shaft 22 of catheter 21 withtip section 40 comprising multiple electrodes 50 (inset 25). In thepresent example, tip section 40 comprises a Lasso® catheter, alsoreferred to herein as “lasso” for brevity, produced by Biosense WebsterInc. (Irvine, Calif.). The lasso and electrodes 50 are described indetail with respect to FIG. 2 below.

In other embodiments, tip section 40 may comprise any other suitabletype of deflectable catheter having electrodes 50.

In the embodiment described herein, electrodes 50 are configured toapply IRE ablation pulses to tissue of the left atrium of a heart 26,such as IRE ablation of an ostium 51 of a pulmonary vein in heart 26.Electrodes 50 may also be used for sensing intra-cardiacelectrocardiogram (ECG) signals. Note that the techniques disclosedherein are applicable, mutatis mutandis, to other sections (e.g., atriumor ventricle) of heart 26, and to other organs of a patient 28.

In some embodiments, the proximal end of catheter 21 is connected to acontrol console 24 (also referred to herein as a console 24) comprisingan ablative power source, in the present example an IRE pulse generator(IPG) 45, which is configured to deliver peak power in the range of tensof kW. Console 24 comprises a switching box 46, which is configured toswitch the power applied by IPG 45 to one or more selected pairs ofelectrodes 50. A sequenced IRE ablation protocol, also referred toherein as an ablation plan or a predefined pattern, may be defined inadvance by physician 30, or by processor 41, or by a combinationthereof, and stored in a memory 48 of console 24.

In some embodiments, processor 41 and/or physician 30 may select, e.g.,based on electrical mapping of activation pulses produced in heart 26,the most suitable predefined pattern for obtaining the desired outcomeof the IRE ablation procedure. The configuration of tip section 40 withIPG 45 and switching box 46 are described in detail with respect to FIG.2 below, and the predefined pattern is described in detail in FIGS. 2and 3 below.

In some embodiments, a physician 30 inserts distal end 22 a of shaft 22through a sheath 23 into heart 26 of patient 28 lying on a table 29.Physician 30 navigates distal end 22 a of shaft 22 to a target locationin heart 26 by manipulating shaft 22 using a manipulator 32 located, forexample, in close proximity to the proximal end of catheter 21. Duringthe insertion of distal end 22 a, deflectable tip section 40 ismaintained in a straightened configuration by sheath 23. By containingtip section 40 in a straightened configuration, sheath 23 also serves tominimize vascular trauma when physician 30 moves catheter 21, throughthe vasculature of patient 28, to the target location, such as anablation site in heart 26.

Once distal end 22 a of shaft 22 has reached the ablation site,physician 30 retracts sheath 23 and manipulates shaft 22 to placeelectrodes 50 disposed over the lasso of tip section 40 to make contactwith the walls of ostium 51 at the ablation site. In the presentexample, the ablation site comprises a pulmonary vein, but in otherembodiments, physician 30 may select any other suitable ablation site.

In some embodiments, electrodes 50 are connected by wires runningthrough shaft 22 to the processor 41, which is configured to controlswitching box 46 of interface circuits 44 in console 24.

As further shown in inset 25, distal end 22 a comprises a positionsensor 39 of a position tracking system, which is coupled to distal end22 a, e.g., at tip section 40. In the present example, position sensor39 comprises a magnetic position sensor, but in other embodiments, anyother suitable type of position sensor (e.g., other than magnetic-based)may be used. During the navigation of distal end 22 a in heart 26,processor 41 of console 24 receives signals from magnetic positionsensor 39 in response to magnetic fields from external field generators36, for example, for the purpose of measuring the position of tipsection 40 in heart 26 and, optionally, displays the tracked positionoverlaid on the image of heart 26, on a display 27 of console 24.Magnetic field generators 36 are placed at known positions external topatient 28, e.g., below table 29. Console 24 also comprises a drivercircuit 34, configured to drive magnetic field generators 36.

The method of position sensing using external magnetic fields isimplemented in various medical applications, for example, in the CARTO™system, produced by Biosense Webster Inc. (Irvine, Calif.) and isdescribed in detail in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118,6,239,724, 6,618,612 and 6,332,089, in PCT Patent Publication WO96/05768, and in U.S. Patent Application Publication Nos. 2002/0065455A1, 2003/0120150 A1 and 2004/0068178 A1, whose disclosures are allincorporated herein by reference.

Typically, processor 41 of console 24 comprises a general-purposeprocessor of a general-purpose computer, with suitable front end andinterface circuits 44 for receiving signals from catheter 21, as well asfor applying ablation energy via catheter 21 in a left atrium of heart26 and for controlling the other components of system 20. Processor 41typically comprises software in memory 48 of system 20, which isprogrammed to carry out the functions described herein. The software maybe downloaded to the computer in electronic form, over a network, forexample, or it may, alternatively or additionally, be provided and/orstored on non-transitory tangible media, such as magnetic, optical, orelectronic memory.

Applying Irreversible Electroporation Pulses to Tissue

Irreversible electroporation (IRE), also referred to as Pulsed FieldAblation (PFA), may be used as a minimally invasive therapeutic modalityfor forming a lesion (e.g., killing tissue cells) at the ablation siteby applying high-voltage pulses to the tissue. In the present example,IRE pulses may be used for killing myocardium tissue cells in order totreat cardiac arrhythmia in the heart 26. Cellular destruction occurswhen the transmembrane potential exceeds a threshold, leading to celldeath and thus the development of a tissue lesion. Therefore, ofparticular interest is the use of high-voltage bipolar electricalpulses, e.g., using a pair of electrodes 50 in contact with tissue atthe ablation site, to generate high electric fields (e.g., above acertain threshold) to form a lesion by killing tissue cells locatedbetween the electrodes.

In the context of this disclosure, “bipolar” voltage pulse means avoltage pulse applied between two electrodes 50 of catheter 21 (asopposed, for example, to unipolar pulses that are applied, e.g., duringa radio-frequency ablation, by a catheter electrode relative to somecommon ground electrode not located on the catheter). Moreover, theterms “IRE pulse” and “bipolar ablation pulse” are used interchangeablyand refer to one or more bipolar pulses applied by IPG 45, via switchingbox 46 and an electrode-pair (EP) selected from electrodes 50, to theablated tissue of heart 26.

To implement IRE ablation over a relatively large tissue region of heart26, such as a circumference of an ostium of a pulmonary vein (PV) or anyother suitable organ, it is necessary to use multiple pairs ofelectrodes 50 of catheter 21 having multi electrodes 50 in tip section40. To make the generated electric field as spatially uniform aspossible over a large tissue region it is best to have pairs ofelectrodes 50 selected with overlapping fields, or at least fieldsadjacent to each other. However, there is a Joule heating component thatoccurs with the IRE generated fields, and this heating may causeuncontrolled damage to tissue and undesired damage to the electrodeswhen multiple pairs of electrodes 50 are continuously used for applyingthe predefined the IRE pulses in accordance with a pattern of timeslots.

In some embodiments, based on pre-mapping of activation signals producedin heart 26, processor 41 is configured to assist the physician 30 indefining the IRE ablation plan. The pre-mapping may be carried out usingelectrodes 50, and/or using surface electrodes 38, shown in the exampleof FIG. 1, as attached by wires running through a cable 37 to the chestand shoulder of patient 28.

In some embodiments, surface electrodes 38 are configured to sensebody-surface (BS) ECG signals in response to beats of heart 26.Acquisition of BS ECG signals may be carried out using conductive padsattached to the body surface or any other suitable technique. As shownin FIG. 1, surface electrodes 38 are attached to the chest and shoulderof patient 28, however, additional surface electrodes 38 may be attachedto other organs of patient 28, such as limbs.

In some embodiments, electrodes 50 are configured to sense intra-cardiac(IC) ECG signals, and (e.g., at the same time) surface electrodes 38 aresensing the BS ECG signals. In other embodiments, sensing the IC ECGsignals may be sufficient for performing the IRE ablation, so thatsurface electrodes 38 may be applied for other use cases.

In some embodiments, physician 30 may couple multiple electrodes 50 to atarget tissue at the ablation site in heart 26. The target tissue isintended to be ablated by applying one or more IRE pulses via pairs ofelectrodes 50. Note that the IRE pulses may be applied to the targettissue multiple times, using any suitable pattern, during the IREablation procedure.

This particular configuration of system 20 is simplified for the sake ofconceptual clarity and is shown by way of example, in order toillustrate certain problems that are addressed by embodiments of thepresent invention and to demonstrate the application of theseembodiments in enhancing the performance of such an IRE ablation system.Embodiments of the present invention, however, are by no means limitedto this specific sort of exemplary system, and the principles describedherein may similarly be applied to other sorts of ablation systems.

Applying Irreversible Electroporation Pulses to Tissue in Accordancewith a Predefined Pattern

FIG. 2 is a schematic pictorial illustration of tip section 40, and anarchitecture for applying IRE pulses to selected electrodes 50, inaccordance with an exemplary embodiment of the present invention.

In the example of FIG. 2, tip section 40 comprises ten electrodes 50,referred to herein as electrodes 50A, 50B, 50C, 50D, 50E, 50F, 50G, 50H,50I and 50J, coupled to tip section 40 along the lasso described in FIG.1 above.

In some embodiments, IPG 45 applies the BAPs to switching box 46, whichis electrically coupled to each of electrodes 50A-50J via a respectivewire 55, or using any other suitable connection.

In some embodiments, based on the aforementioned mapping of heart 26,processor 41 and/or physician 30 may select from the aforementioned oneor more predefined patterns of the IRE ablation protocol stored inmemory 48, the most suitable predefined pattern for treating thearrhythmia detected in heart 26.

An example of a predefined pattern is shown in Table 1 below:

TABLE 1 Predefined pattern of EP by time slot Time Slot Energized EP 1 50E-50G 2  50F-50H 3 50A-50C 4  50B-50D 5 Empty 6 Empty 7 50G-50I  850H-50J  9 50C-50E 10 50D-50F 

As shown in Table 1, each time slot defines an electrode-pair (EP),which receives bipolar ablation pulses (BAPs) generated by IPG 45 androuted to the respective EP via switching box 46.

In some embodiments, all EPs have the same inter-electrode distance. Forexample, the distance between electrodes 50E and 50G of time slot 1 issimilar to the distance between electrodes 50F and 50H of time slot 2,and to the distance between electrodes 50C and 50E of time slot 9.

In some embodiments, at least some of electrodes 50 are used more thanone time in different time slots of the same predefined pattern, but ispaired with a different electrode in different time slots. For example,electrode 50C is paired with electrode 50A in time slot 1, and withelectrode 50E in time slot 9. Moreover, as shown in Table 1, at leastone time slot is positioned, in the predefined pattern, between two timeslots having a common electrode.

In some embodiments, the time slots are applied sequentially to theablated tissue, but in other embodiments, two or more time slots may beapplied at the same time or with some overlap in timing.

In some embodiments, each time slot defines a waveform of one or moreBAPs that are applied in bursts, to the tissue by the respective EP. Inthe present example, the waveform comprises ten pulses of about 5microseconds each, applied at 200 KHz, and the time slot is concluded bya time gap of about 0.5 millisecond (msec) typically but not necessarilyscheduled after the tenth pulse. Moreover, all the time slots of Table 1are using the same waveform described above.

In the context of the present disclosure and in the claims, the terms“about” or “approximately” for any numerical values or ranges indicate asuitable dimensional tolerance that allows the part or collection ofcomponents to function for its intended purpose as described herein.

In some embodiments, the predefined pattern comprises a periodic set ofthe time slots. In other words, after concluding time slot 10 and thetime gap, the predefined pattern is repeated one or more times, so as tocomplete the required amount of ablation energy applied to the ablatedtissue. Note that the number of repetitions may be calculated based onthe electrical mapping and the aforementioned ablation protocol. Asdescribed above, the total duration of each time slot is slightly longerthan about 0.5 msec, and therefore, the total duration, also referred toherein as the cycle length, of the predefined pattern, is slightlylonger than 5 msec.

In such embodiments, each electrode-pair of the predefined pattern has aduration slightly longer than 5 milliseconds for cooling beforereceiving the next waveform of ten BAPs, thereby preventing overheatingof the respective electrodes, and may also prevent uncontrolled damageto the section of tissue located between the electrodes of therespective pair.

In some embodiments, the predefined pattern of Table 1 has time slots 5and 6 that are empty. In the context of the present disclosure and inthe claims, the term “empty” refers to not applying any BAP to any EP ofelectrodes 50 of catheter tip 40. Note that in the present example, thetime gap of 0.5 msec is retained also in the empty time slots.

Note that the EPs of the predefined pattern are interleaved between thetime slots. For example, electrode 50F of time slot 2 is positioned(along catheter tip 40) between electrodes 50E and 50G of time slot 1.

In other embodiments, the ablation protocol may comprise a predefinedpattern having all time slots filled with respective EPs receiving oneor more BAPs from IPG 45. In other words, without empty time slots.

In yet other embodiments, physician 30 and/or processor 41 may skip atime slot, e.g., by not energizing the EP defined in the time slot, andthereby may shorten the cycle length of the predefined pattern.

In alternative embodiments, each time slot may comprise more than onewaveform with a time gap between adjacent waveforms.

This particular time slot configuration and order of the predefinedpattern of Table 1 are shown by way of example, in order to illustratecertain problems that are addressed by embodiments of the presentinvention and to demonstrate the application of these embodiments inenhancing the performance of such an IRE ablation protocol. Embodimentsof the present invention, however, are by no means limited to thisspecific sort of example predefined pattern, and the principlesdescribed herein may similarly be applied to other sorts of predefinedpattern and/or ablation protocols.

FIG. 3 is a flow chart that schematically illustrates a method forapplying bipolar IRE ablation pulses to ablated tissue, in accordancewith an embodiment of the present invention. The method begins at anablation protocol definition step 100, with defining a pattern ofablation protocol having a periodic set of time slots. Each time slotcomprising an electrode-pair (EP), a waveform of one or more bipolarablation pulses (BAPs), and duration of the time slot. As described inFIG. 2 above, the time slot may comprise a time gap scheduled before orafter the one or more BAPs of the waveform.

At a catheter insertion step 102, physician 30 inserts catheter tip 40of catheter 21 into heart 26 and positions multiple electrodes 50 incontact with the target tissue, as described in FIG. 1 above.

At a tissue ablation step 104 that concludes the method, irreversibleelectroporation (IRE) bipolar ablation pulses (BAPs) are applied to thetarget tissue in accordance with the predefined pattern of the ablationprotocol described in step 100 above, and in greater detail in FIG. 2above. Note that the predefined pattern is periodic, such that the setof time slots repeats after concluding the cycle of time slots definedin the pattern. The number of repetitions is defined based on theablation protocol and the electrical mapping of heart 26, such that, incase of multiple repetitions, the method terminates after concluding thelast repetition, and physician 30 retracts catheter tip 40 out ofpatient 28.

Although the embodiments described herein mainly address irreversibleelectroporation of patient heart, the methods and systems describedherein can also be used in other applications, such as but not limitedto renal ablation, liver ablation, treatment of lung cancer or inablation of any other suitable organ.

It will thus be appreciated that the embodiments described above arecited by way of example, and that the present invention is not limitedto what has been particularly shown and described hereinabove. Rather,the scope of the present invention includes both combinations andsub-combinations of the various features described hereinabove, as wellas variations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot disclosed in the prior art. Documents incorporated by reference inthe present patent application are to be considered an integral part ofthe application except that to the extent any terms are defined in theseincorporated documents in a manner that conflicts with the definitionsmade explicitly or implicitly in the present specification, only thedefinitions in the present specification should be considered.

1. A method for applying bipolar ablation pulses, the method comprising:positioning multiple electrodes of a catheter in contact with tissue ofan organ; and ablating the tissue using the multiple electrodes inaccordance with a predefined pattern comprising a periodic set of timeslots, wherein each of the time slots defines (i) an electrode-pair(EP), (ii) a waveform of one or more bipolar ablation pulses (BAPs)applied to the tissue by the EP, and (iii) a duration of the time slot,wherein the time slots are applied sequentially, and wherein the patternfurther comprises at least one time slot that is empty.
 2. The methodaccording to claim 1, wherein a first electrode of a first EP ispositioned between second and third electrodes of a second EP.
 3. Themethod according to claim 1, wherein each of the time slots comprises atime gap scheduled before or after the one or more BAPs.
 4. The methodaccording to claim 1, wherein the BAPs comprise irreversibleelectroporation (IRE) BAPs.
 5. The method according to claim 1, whereinthe EPs of the time slots have a same inter-electrode distance.
 6. Themethod according to claim 1, wherein a first EP of a first time slot ofthe predefined pattern comprises a first electrode and a secondelectrode, and wherein a second EP of a second time slot of thepredefined pattern comprises the first electrode and a third electrode.7. The method according to claim 6, wherein the predefined patterncomprises at least one time slot positioned between the first and secondtime slots.
 8. The method according to claim 1, wherein positioning thecatheter comprises positioning a lasso catheter.
 9. A system forapplying bipolar ablation pulses, comprising: a catheter comprisingmultiple electrodes, which are configured to make contact with tissue ofan organ; a pulse generator, which is configured to generate one or morebipolar ablation pulses (BAPs); and a processor, which is configured toablate the tissue using the multiple electrodes in accordance with apredefined pattern comprising a periodic set of time slots that areapplied to the tissue sequentially, wherein each of the time slotsdefines (i) an electrode-pair (EP) selected from the multipleelectrodes, (ii) a waveform of the one or more BAPs applied to thetissue by the EP, and (iii) a duration of the time slot, and wherein thepattern further comprises at least one time slot that is empty.
 10. Thesystem according to claim 9, wherein a first electrode of a first EP ispositioned between second and third electrodes of a second EP.
 11. Thesystem according to claim 9, wherein each of the time slots comprises atime gap scheduled before or after the one or more BAPs.
 12. The systemaccording to claim 9, wherein the BAPs comprise irreversibleelectroporation (IRE) BAPs.
 13. The system according to claim 9, whereinthe EPs have a same inter-electrode distance.
 14. The system accordingto claim 9, wherein a first EP of a first time slot of the predefinedpattern comprises a first electrode and a second electrode, and whereina second EP of a second time slot of the predefined pattern comprisesthe first electrode and a third electrode.
 15. The system according toclaim 14, wherein the predefined pattern comprises at least one timeslot positioned between the first and second time slots.
 16. The systemaccording to claim 9, wherein the catheter comprises a lasso catheter.